brand new petrol mower rapidly cuts out

Hi., I just bought a brand new petrol mower this weekend. I measured and filled the oil and petrol correctly. Its a 4 stroke engine

It starts without too much difficulty (though not as easy as Id expected). After mowing for maybe 30 seconds, the motor rapidly fades and then stops. At this point the starting cord is very tough to pull, and I generally have to leave it for a while before I can start it as easily as before.

Im not sure what Im doing wrong or why its cutting out. Someone suggested Id put in too much oil, but I followed the instructions and dont see any smoke indicative of oil burning off

Its my first petrol mower so Im a bit unsure what else could be wrong. Any advice appreciated

Cheers Carpii

Reply to
Carpii
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Sounds like the choke isn't working and it's flooding itself.

Reply to
EricP

you /have/ switched the fuel tap on, haven't you ?

Reply to
.

If the engine is getting tight as you describe it indicates it is seizing due to lack of oil. How you square this with having filled the oil correctly I don't know but, if it were a fuel problem as others have suggested, the engine would not be tight. Without looking at it it is difficult to help but I would siggest, at least, getting a second opinion on the oil filling.

Reply to
Bob Mannix

That sounds like a blockage in the fuel system somewhere...

It's likely to smoke a lot if it's too full. Check that there is enough oil, and you've put it in the correct hole. There should be a way of checking the level, see the handbook (what sort of mower is it AAMOI?).

If it's got the right amount of the correct oil in it then it sounds like a fault (no ring clearance?), and it might be best to take it back!

However, look in the book!

Reply to
Chris Bacon

Daft assumption I know, but you ARE keeping hold of the 'Dead Mans Handle' aren't you?

HTH

John

Reply to
John

As others have said check the oil and fuel levels. There probably isn't a choke or fuel valve but that depends on the engine and mower.

Another possibilty is that the brake that quickly stops the engine rotating when you release the dead mans handle isn't releasing properly and after a while heats up and binds on hard enough to stall the engine.

You are operating the deadmans handle when starting? I think you must be as the engine runs and they normally short the magneto out as well killing the spark. Check that the brake is coming off properly.

Reply to
Dave Liquorice

Thats true as their will be pressure still in the piston chamber and leaving it a while,the pressure is gradually diminishing.

Are keeping your fingers on the throttle evenly as your cutting?

If in doubt take it back.

Reply to
The3rd Earl Of Derby

Nothing to do with pressure in the chamber then? It being brand new an all. ;-)

Reply to
The3rd Earl Of Derby

Blocked vent on the fuel tank (in the filler cap)?

Reply to
Bob Eager

He said "very tough to pull" so I would say not (as you ask ). The pressure will release as soon as a valve opens, which will be after a small fraction of a revolution, after which there will be no pressure - unitl - the main pressure is built up during the compression stroke (obviously, the clue is in the name) which will be the same whether it has just been running or has been left for a while. A new mower will have higher compression than an old one but it won't change from minute to minute.

Reply to
Bob Mannix

There will only be pressure in the cylinder if it stops at, or approaching, tdc on the compression stroke. Which it wouldn't. Ever. It should not be any harder to start whether it's been running or not, in fact it will start easier if it's warm for obvious reasons.

It's either partially seizing due to lack of oil, which seems unlikely as it would probably keep running until it did seize properly, or the dead man's handle is binding somehow when it's warm.

OP: Take it back to the shop.

Si

Reply to
Mungo "Two Sheds" Toadfoot

Too true, sounds like it is seizing. If you are using two stroke in a four stroke engine, it will choke up until the oil drains out. It will eventually soot up the plug.

There is a minor chance of it clonking due to a weak mixture as the unburned oil counts as petrol starvation. It's only an interesting accademic point for model airplane engines though. : What mix of oil and petrol are you using, Carpii?

The tank valve is probably blocked. You will find it runs for a little longer on a near empty tank than on a full one if that is so but just clean the vent rather than miss around with it. Also, check the air filter is clean.

As long as there is some oil in the crank case there is no problem with the oil situation. If you take the plug out its colour will tell you if the mixture is too oily, too rich or whatever. If it's not that then it might be te timing. This will "go out" if you mow a brick or something.

I wouldn't mess around with anything technical, just take it back if it's not the vent or air filter.

Reply to
Weatherlawyer

Happened on my mower. Missus had a go while I was in hospital. Put the cap off the petrol can on top of the mower & vice versa. Ran until it pulled a vacuum and then cut out.

Reply to
Bookworm

He SAID its a 4-stroke...

It could be many many things.

My guess would be he hasn't released the choke. Or has released it too soon.

If its full of ordinary engine oil, which it should be, its not gonna seize.

These things are only splash lubricated y'know. No oil pump etc etc.

Reply to
The Natural Philosopher

Ah but does he know that you don't (generally) put the oil in the petrol with a 4 stroke...

My mower doesn't have a choke as such just a primer bulb which you push a few times. This squirts extra fuel into the carb to get it going from cold. These little air cooled engines need very little choke even if manually operated.

Reply to
Dave Liquorice

What make of mower is it, ive heard that the Chinese manufactured engine in the Challenge/Power devil type mower is extremely unreliable.

You did put the oil in the crankcase and not mixed with the petrol ?

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Reply to
Mark

Lets go through thisa one step at a time and check things systematically even if it involves some apparantly silly checks (sorry) - the post is slightly ambiguous when you say that you "measured and filled the oil and petrol correctly" - does this mean that you prepared an oil and petrol mixture correctly and put this into the fuel tank. If so this is a 2-stroke mix for 2-stroke engines where as you have a 4-stroke mower. This needs normal unleaded petrol in the tank and oil is added separately to the crank case at another location.

Next check the oil level - every 4 stroke engine I have seen has an oil filler with a dipstick. Put the mower on a level surface and allow to stand for a while. remove the dipstick, wipe it replace and remove to take a reading - it should not be too full or too empty which you can check via the marks on it. Also check that you used the appropriate oil.

If this is all OK then the engine shoudl not be harder to "crank" when it stops than when cold - as others have said this woudl be due to lubrication problems. If it is then there is a serious fault with the engine and you should return to the seller.

Other posters have made other suggestions as to what may be causing it to stop. How are you using the choke? On most mowers it is only needed for a few seconds when the engine is first started - the engine will run rough, stutter and perhaps even stall if it is left on.

How does the engine fade - does it miss, stutter and stall? Does it labour as if under a lot of laod whic eventuially overcomes the power of the engine? There is often a clue to the fault there.

You presumably have checked and worked through the instructions. If you can't get it going and can't find the fault by going through the above then take it back.

HTH

Reply to
hzatph

Hi all, thanks for all the ideas and suggestions. Ill try and answer them all but its a bit tricky to 'quote' them

Engine is definitely a 4 stroke. It has seperate oil and petrol reservoirs, and I havent mixed oil/petrol like I understand you do with

2-strokes. The oil being used is B and Q 4 stroke lawnmower oil.

Im holding down the dead mans handle constantly while mowing, its not stopping as a result of me leaving go. Admittedly it took me a few goes to understand this though hehe

I dont think it has a choke as such. Does that make any sense? Ill double check this. The pushbar has a control lever on it, saying 'slow, fast, start'. Maybe the 'start' setting is equivalent to the choke ? I start the mower and then move this lever to fast, mow for a bit and it generally cuts out after 30 seconds of this. There is no backfiring or spluttering, it simply starts slowing down and then stops, in the space of 4 or 5 seconds.

I guess it could be described as this yes. The grass isnt very long, but theres bits of uncollected grass lying about from when my electric mower packed in. It doesnt look as if it should cause an engine much difficulty though.

Ive read the instruction manual and and following them pretty much to the letter.

I bought it from B and Q, and given the choice between a mountfield and this one, I chose this one because it could collapse a bit smaller (Im limited for space in my shed.) Sorry, I dont know the brand at the moment, but Im going to be trying with it again today so Ill find out.

Likewise, I havent checked the oil using the dipstick, but I will today. But I did check it was empty before filling it, and put 600ml in as the manual suggested. Also put in 1 litre of unleaded petrol.

Im off give it another go, Ill come back with engine power and brand if its still struggling.

Thanks guys Paul

Reply to
Carpii

Sounds like fuel starvation..try running briefly with the petrol cap OFF the tank..also make sure that the lever is not still in the start position...or try running with it there for a while first to let the engine fully warm up.

Any signs of smokiness at all?

Hmm. Depends on how good the engine is

Always a mistake ;-)

Other than a partially blocked jet, or a vaccum in teh tank causing fuel stravation, I can;t see what it could be.

Maybe time to take it back and say 'it doesn't work.

Reply to
The Natural Philosopher

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